An experiment I've always been interested in trying, but lack the tools to carry out, is to take a nice dry unsplit log and drill/file the core out of it in a somewhat conical vent shape. It would be interesting to see what it would look like if you could get the log burning on the inside with the axis vertical and good space for airflow underneath.

This is only related insofar as the term 'rocket stove' reminded me of the plan, but I thought it was worth sharing in case anyone with a woodworking router in their garage wanted to give it a try.